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© 2012 AOAC INTERNATIONAL

AOAC O

FFICIAL

M

ETHODS

OF

A

NALYSIS

(2012)

M

ICROBIOLOGY

G

UIDELINES

Appendix J, p. 17

ANNEX E

Example of Graph of POD Values from

Qualitative Method Single Laboratory Data

Notes

:

(

1

) The concentration plotted should be MPN/test portion.

(

2

) Confidence intervals may also be plotted.

(

3

) Collaborative data should be plotted analogously.

ANNEX F

Calculation of LPOD and dLPOD Values from

Qualitative Method Collaborative Study Data

For a multilaboratory trial where L = number of laboratories, R =

replicates per laboratory, N = LR = total replicates, LPOD estimate

is given by

where

x

is the number of positive results.

Method for estimating LPOD 95% confidence intervals:

Step 1.

—Enter data into AOAC spreadsheet with 1 for positive

response and 0 for negative response. Record the mean LPOD,

s(R), and s(r).

Step 2

.—Calculate s(L), standard deviation due to laboratory

effect as:

2

2

( )

( )

( )

s L s R s r

Step 3

.—Calculate s(POD) as the standard deviation of the

individual laboratory POD estimates.

2

(

)

(

)

1

i

POD LPOD

s POD

L

¦

Step 4

.—Calculate degrees of freedom, df for s(POD) as follows:

2 2

2

2 2

2 2

( )

( )

1

s r

s L

L N

df

s r

s L

N

L

L

N L

ª

º

«

»

«

»

¬

¼

ª

º

ª

º «

»

«

» «

»

¬

¼ ¬

¼

Step 5

.—Calculate 95% confidence limits on LPOD:

If 0.15 ≤ LPOD ≤ 0.85:

ANNEX D

Summary Data Table for Qualitative Method Single Laboratory Studies

Table D1. Comparative results for the detection of

Listeria innocua

in raw shrimp

Concentration

Candidate presumptive (CP)

Candidate confirmed (CC)

Candidate method (C)

Reference method (R)

C vs R CP vs CC

Statistic

MPN/25 g

N

x POD(CP)

N

x POD(CC)

N

x POD(C)

N

x POD(R)

dPOD(C,R) dPOD(CP,CC)

Estimate

0.00

20

0

0.00

20

0

0.00

20

0 0.00

20

0 0.00

0.00

0.00

LCL

0.00

0.00

0.00

0.00

0.00

–0.16

–0.16

UCL

1.50

0.16

0.16

0.16

0.16

0.16

0.16

Estimate

0.80

20

12 0.60

20

10

0.50

20

10 0.50

20

11 0.55

–0.05

0.10

LCL

0.43

0.39

0.30

0.30

0.34

–0.33

–0.19

UCL

1.39

0.78

0.70

0.70

0.74

0.24

0.37

Estimate

3.00

20

20 1.00

20

20

1.00

20

20 1.00

20

19 0.95

0.05

0.00

LCL

1.58

0.84

0.84

0.84

0.76

–0.12

–0.16

UCL

5.68

1.00

1.00

1.00

1.00

0.24

0.16

Estimate

17.00

20

20 1.00

20

20

1.00

20

20 1.00

20

20 1.00

0.00

0.00

LCL

0.27

0.84

0.84

0.84

0.84

–0.16

–0.16

UCL

1060

1.00

1.00

1.00

1.00

0.16

0.16